Outrage over emails sent by a top aide mocking Muslims, blacks, Latinos, women and others is presenting Los Angeles County Sheriff Jim McDonnell with a serious test as he attempts to reform his troubled agency.

On Thursday, more civil rights groups called for the sheriff to fire or discipline the aide, Tom Angel, after the emails were published by The Times this week.

A person who made light of those stereotypes is unfit for a top position at an agency that polices the very groups he mocked, some civil rights leaders said.

But McDonnell has said he has no immediate plans to discipline his chief of staff because the emails date from Angel’s time with the Burbank Police Department and were an “uncharacteristic act” that do not reflect Angel’s usual good character and judgment.

“Although there is no doubt that such instances, if occurring within the Sheriff’s Department, would result in disciplinary action, there is also no doubt that Chief Angel understands and respects that fact,” the sheriff said in a statement.

McDonnell was elected in November 2014 as an outsider promising to steer the agency past an era in which some deputies beat jail inmates and others were found to have singled out African Americans and Latinos in the Antelope Valley for harassment.

He brought Angel, a veteran sheriff’s official, back from Burbank as a key member of his reform administration. Angel’s departure would mean the loss of a trusted aide who helps McDonnell navigate the Sheriff’s Department’s huge bureaucracy and who has a hand in a broad array of projects.

As a chief, Angel is an at-will employee and could be fired or demoted without the civil service protections of lower-ranking sworn personnel.

Jokes like the ones Angel forwarded from his work account feed into a larger atmosphere of racial bias, which in turn can foster the mistreatment of minority groups in the jails and on the streets, said Peter Bibring, a senior staff attorney at the American Civil Liberties Union of Southern California and director of police practices for the ACLU of California. The organization has called on Angel to step down or be fired.